Posted
by
ScuttleMonkey
on Wednesday April 04, 2007 @05:29PM
from the pie-in-the-sky dept.

withoutfeathers writes "The Economist magazine has an article on Flying wind farms. Mind you, we're not talking about ordinary, terrestrial windmills here. We're talking about actual airborne — up to 10km in the sky — wind farms intended to harvest the immense supply of energy in the jet stream. On the surface, the idea seems a little eccentric but, in fact, San Diego (California, US) based Sky WindPower has, apparently, thought their concept through pretty thoroughly and believes they can not only make this work, but do so profitably. The article discusses several other ideas for high-flying wind farming including a Dutch proposal to use pairs of kites to drive a generator."

Or have the cable on a large pully. And create a redundant subsystem on top of it, that throws out a parachute in case of an emergency. And have an independent computer monitor its position and vector, and throw the emergency switch when one of those values falls outside of safe parameters.

The cable that is tethering it to the ground will be a hazard to aviation and all altitudes below the generator. Not only would the cable be very hard to see, but, unlike power cables and guy wires for antennas, it would also be hard to chart, since I imagine that the generator will move around quite a bit as the jetstream fluctuates.

There already exist no-fly zones all over the place. I don't see why we couldn't just set up a perimeter around the cable as a no-fly zone and planes fly around it, like they would a military base, an erupting volcano, or other such places.

On the ground have a spotlight that lights the cable. Of course thecable will not be as straight as the beam, so the illuminated spotwould have to traverse. The cable itself could have some reflectorsto make this easier, such as like a mirror disco ball -- sometimesthe observer gets lucky to see a really bright light. Usingholographic material, the reflectors could be flush whichwould be needed for winching the balloon/kite back down.

That situation exists today in the form of tethered high-altitude balloons used for border surveillance...I believe there are 15 of them along the US/Mexican border. They have to be charted carefully, but so far the aviation community has dealt with them.

Also the cables would probably become lighting conduits if they are insulators and lighting discharge if they are conductors.
If we are constantly discharging the potential between the earth and the upper atmosphere I would expect this would have profound effects on the weather.

Use the length of cable as a radius and make a cylindrical no-fly zone. A few 10km circles in low-traffic areas shouldn't cause too much of a disruption. For non-commercial pilots, you could mark out the radius with visual aids - though the really dangerous area would be pretty small at low altitudes, and it probably would not be too cost prohibitive to have regular markings for the first few thousand feet of cable.

"Is it even possible for us to tap enough power from the jet stream (or other high altitude winds) to cause problems?"

No. The total power we could possibly harvest with systems like those in the article is not worth mentioning in the scale of the total energy in the jet stream. Windmills take a few percent of the energy of the wind that actually passes over them, wich would only be a tiny fraction of the wind in the jet stream.

I am not. I have a degree in Mathematics in which I made a particular study of chaotic dynamical systems. I've written papers about the Butterfly effect; I've constructed physical models that demonstrate it. Let me tell you about the Butterfly Effect, so that you can refrain from bringing it up in discussions such as this in the future:

In a system which exhibits sensitive dependence on initial conditions (such as the weather), you cannot predict the details of long-term behavior (will there be a tornado in Iowa exactly 1 year from today) because tiny variations, well below what your measurement of the system could possibly account for (such as the breeze generated by the flapping of butterfly wings) will cause reality to drift further and further out of synch with your model until there is no resemblance on the detail level.

So the butterfly effect makes it impossible to ever predict what day it will rain months in advance, for example. But it does not prevent predictions about the aggregate, macroscopic behaviour of the system as a whole. In Meterological terms, long term weather prediction is impossible, but short-to-mid term climate prediction is easy.

Lets be ridiculously generous, and say this system takes a thousanth of a percent of the wind energy in the jet stream out. Is it reasonable to suppose this might cause significant changes in the world climate that will make a huge difference in its suitability for humans? No; it is not remotely reasonable. It's just not enough energy to make much difference.

Would it mean sometime in the future there will be a thunderstorm one day and not another? Absolutely. Whether you exhale the next breath you take slowly or forcefully means exactly the same thing; the minute difference in the velocity of a few thousand molecules of air your breathing pattern makes will eventually mean the difference in what day you get a thunderstorm.

The relevance of the Butterfly Effect in deciding whether to build this wind farm is the same as its relevance in deciding how forcefully to exhale your next breath. It means that the exact effect of either cannot be predicted, and that's it. It's not a reason to not do anything. (Well, except things like attempting long term prediction of weather detail.)

I am also a mathematician and I can tell you that the concern is whether or not our "minute" impact will tip the system over a threshold and toward a chaotic attractor which represents an undesirable state (e.g. a shift of the jetstream to a lower potential state which results in altered rainfall or temperature patterns in agricultural areas of the world).

What you said about the Butterfly Effect is correct but deals with the impact of small random fluctuations on a chaotic system. In this situation the planned alteration is highly non-random (a consistent reduction in energy potential of the jetstream), and the inevitable consequence of success is a gradual and significant increase in the magnitude of the change. The Butterfly Effect is not the correct model for non-random state changes of increasing magnitude.

In other words, the quoted person is thinking about a valid concern, but used the wrong model to express it. The concern is still valid however. Will our actions disturb a delicate balance in nature of which we are not yet aware? We just don't know. Experiments of this scope are not the ones that you want to go the wrong way, so I sincerely hope that this company and the government spends as much time determining how to calculate the limit of what we allow ourselves to pull from the jetstream as we do figuring out how to do it.

Windmills take a few percent of the energy of the wind that actually passes over them, wich would only be a tiny fraction of the wind in the jet stream.

Even of the wind that actually passes through the area "swept" by the blades, the max it can harvest is about 59.3%. This is the "Betz Limit", the aerodynamic counterpart of the Laugher Curve of government revenue versus tax rates:

- Extracting power slows and deflects the air.
- Slowing and deflecting the air reduces the amount of moving air you can extract power from.
- Don't slow/deflect it and you get no power, stop it completely and you get no air - and thus no power. Zero at both ends, non-zero between. Somewhere there's a maximum.
- The maximum (for compressible fluids in free space) is where you extract 16/27ths of the energy from the air you affect (which is essentially the stream of air that passes through the area swept by the blades).

Real turbines can get very close to that, and most of the shortfall is a bit of energy left as rotation and turbulence in the wake.

Hmmm, I was under the impression real turbines didn't get very close to the theoretical maximums at all. But OK, let's call it 60% of the air that passes through the swept area, and let's call that swept area something ridiculously big, like 100,000 square meters (about 25 football fields). With just the core, fastest winds of the jet stream being about 300 miles wide by 3 miles thick, that will extract, by my calculations, 0.0026% of the total energy. I'm not worried.

I'd honestly be more concerned with global warming killing the jet stream than this. The jet stream is largely the result of low-altitude/surface-level thermal gradients (ie the equator to pole temperature difference). Given that most climate models predict the poles will warm significantly more than the equator, if they turn out to be correct I'd say that's far more troubling to the jet stream than a few big kites.

The SHPEGS [shpegs.org] project is an initiative to design and build a system that uses a combination of direct and indirect solar collection to generate electricity and store thermal energy in an economical, environmentally friendly, scalable, reliable, efficient and location independent manner using common construction materials.

I once had a similar idea: to pull energy right out of the air. Here's what I would do: separate a sealed chamber into two subchambers with a little door between them that could be opened. Have some kind of monitor determine *just* the right time to open it so as to increase the pressure in one side. When the pressure difference is large enough? Have one side expand against the other, drawing out useful work. End result? Both chambers have the same pressure *which is less than atmosopheric*! So to recharge, I just open it up to the atmosphere, and start over again.

Go, me, right?

After a few days of this, I woke up to find a severed horse's head in my bed. A note attached to it said. "You're depressurizing the atmosphere. Stop."

Reminds me of a story about the Shortstack. The idea is you build a very, very tall tube that ends where the air pressure is significantly lower. Unsealing the bottom of the tube at ground level than causes the higher pressure air to be sucked upwards where it is a near vacuum. This would introduce an entirely new cycle of circulation and clear polluted cities where the air is trapped by ground features.Of course, the original proponent seemed to miss out that the air in the tube might be affected by gra

What are chances that the geographical areas where these contraptions are installed get hit by bad weather (i.e. typhoons, tornados, hurricanes, hailstorms, lightning, etc)?

They're in the jet stream. That's up at the TOP of the troposphere. The turbulent violence you're talking about happens further down - the top mostly just has winds, and the jet stream is already the worst of it.

Assuming the power station comes down in any uncontrolled fashion, and from the heights they are talking about and the strong jet stream winds they are dealing with, the power generation station could potentially travel many miles before it hits ground, endangering a very very large area below.

Now that would depend on the type of elevated structure. But most of them have acceptable failure mechanisms.

For instance: The four-bladed "helicopter" should auto-gyro nicely. If it loses its tether the blades keep spinning and keep providing lift - in the correct direction even. By transferring power from one blade to another as needed you can navigate it like a glider - even upwind, trading altitude for blade momentum as you drop. This lets you fly it to a landing area, landing vertically and quite gently, even without any additional power source onboard. Or find an updraft and soar until any crummy weather at ground level has moved on.

For instance: The four-bladed "helicopter" should auto-gyro nicely. If it loses its tether the blades keep spinning and keep providing lift - in the correct direction even. By transferring power from one blade to another as needed you can navigate it like a glider - even upwind, trading altitude for blade momentum as you drop. This lets you fly it to a landing area, landing vertically and quite gently, even without any additional power source onboard. Or find an updraft and soar until any crummy weather at

got a buddy that has his pilots license, and was telling me that his teacher taught him how to "bump start" an airplane. Basically, gain enough altitude, shut off the engine, enjoy peace and quiet for a few seconds then go into a dive. Once you have enough air speed, the engine will kick over.Funny thing (and this is what relates to your post) is that he is now training for his helicopters license, and they are teaching the same thing. If you need to re-start the engine, change pitch of the rotors to "do

Everyone I know calls this simply, go figure, a "windmilling prop". You don't even have to go into a dive - windmilling speeds with no power on even something as small as a C172 at best glide - around 60kts - is over 1000 RPM, which is more than enough to start the engine (its capable of starting at less than 100 RPM).

And for the other poster here that thinks you have to "reverse the pitch" of prop blades to get it to windmill...nope. You can do this with a prop that can't change its p

Hey, lets put a bunch of aircraft up at 10km, with cables that tie them to the ground! Excellent idea! Why didn't anyone think of this before?Oh, that's right - they did. They used them to prevent aircraft from flying over towns/cities/military targets (it sort of worked).

It also doesn't seem to make a whole lot of sense to stick a bunch of obstacles up in the jet stream. You know, where airliners tend to like to fly (at least when going west to east).

"They used them to prevent aircraft from flying over towns/cities/military targets (it sort of worked)."Yes, very large numbers of balloons each of which had very large numbers of unmarked trailing cables, which were moved around a lot without telling the enemy where they were, were vaugely successful in making aircraft that wished to attack specific small targets fly at a different altitude. (those balloons were not at 10Km, but low to the ground, and only made the attackers fly a bit higher, where they co

Well, the technical hurdle is capturing the energy from a massive electrical discharge and then releasing it in a controlled form. You can't just send it through some super transformer to knock down the voltage because, even if you could, the voltage rise/fall time is so fast that the inductive impedance of the transformer would probably make it quite ineffective. Even if you could down convert the voltage of the lightning, you'd have difficulty building a device that could accept such a large inrush of

Well, the technical hurdle is capturing the energy from a massive electrical discharge and then releasing it in a controlled form

Build a very large capacitor with it's positive pole at the anchor point. If you build it large enough you might be able to keep it from melting. Large glass Leyden jars? A cap is a cap (you should see the ones I used to build my Interociter) but the methods, conductors and dielectrics can differ widely. Surround the base with induction coils to grab lumps of current that lea

A typical lightning strike is around a thousand kWh. That'll keep a 100W light bulb lit for a few months, but given that your air turbine gizmo will likely only get a few strikes per month, it's hardly worth the effort to capture considering how much wind energy it'll be capturing during that time.

It's best to just treat the lightning a like a nuisance and try to dissipate it safely.

The jet stream is instumental in pushing storm systems around, but is itself a fairly stable, continuous flow at a higher altitude than the storms.

The tethers will keep these continuously grounded, so any static is just some bonus power. The teathers will be great lightning rods, which will probably be more power at once than can be made usable, but it is entirely possible to design them so it's not destructive either.

Ice build up would have to be dealt with, but, hey, it's a power station, if nothing better, heat the cable.

There are definitely technical hurdles to overcome; this is at the conceptual daydreaming stage so far. But the obvious problems seem entirely doable to me.

I'd say the big issue is if you can get reliability good enough that maintenance costs don't kill your cost effectiveness.

They are stable in that there are always jet streams and they follow predictable patterns and don't suddenly drop off. Unfortunately they do move quite a bit. IIRC they tend to start at the poles and head toward the equator making them pretty much unusable for flying a big metal kite.

I'd also say that the energy cost of raising a 10km insulated power cable into the air would also need to be resolved too.

Why would the cable need to be insulated ? Use alternating power through a bare steel wire, and just shield the transformers at each end so they won't get fried if lightning strikes. That way you don't need multiple wires and can use the tether itself as the power cable, allowing you to use very high voltages to minimize power losses.

Well, FWIW, I *DID* read the story. Guess what? There's no mention of any of these issues in it. Wouldn't it be appropriate to bring them up for discussion? The article reads pretty much like the typical Popular Science/Popular Mechanics hype, touting the "coolness factor" and pretty much glossing over some of the other hurdles that would make something like this feasible for mass implementation.

I'm not objecting that what this handful of people are proposing is "wrong." I'm just making light of so

On the surface, the idea seems a little eccentric but, in fact, San Diego (California, US) based Sky WindPower has, apparently, thought their concept through pretty thoroughly and believes they can not only make this work, but do so profitably.

Translation:

This is a totally fucked up idea that has no hope of becoming reality. However, certain venture capitalists that have the ears of certain elected officials, retired milirary leaders, and recent political appointees think that this is certainly worthy of (1) government contracts, (2) earmarks in military spending bills, and (3) "grants" from the DOE, Military, and any other government agency that has a large amount of government gave-a-way cash to burn.

This is a totally fucked up idea that has no hope of becoming reality. However, certain venture capitalists that have the ears of certain elected officials, retired milirary leaders, and recent political appointees think that this is certainly worthy of (1) government contracts, (2) earmarks in military spending bills, and (3) "grants" from the DOE, Military, and any other government agency that has a large amount of government gave-a-way cash to burn.

According to this public disclosure meeting in 2001, whereby high ranking government officials, very senior ex-military, black project staff, and ex-NASA employees pointed out... Zero point energy (aka. free energy) devices already exist, and have for decades, but are hidden by secret black project government programs due to the massive economic impact it would have on the world (i.e. no more need for OIL).

It's time USA citizens wrote their congress men and appealed for all of these senior government etc officials to have a chance to testify under oath as they have promised to do. To date the disclosure project has over 400 such officials willing to testify. This is not wacko conspiracy theorists coming up with crazy theories... it's about the largest government cover up in the history of the modern world.

Adeptus.

PS. If the above is not enough to motivate you, think about how a world without burning fossil fuels would end the global warming impact nearly overnight! The evidence is simply overwhelming. See the video for yourself.

... what about the power transfer cable? I can't imagine a cable that can carry 10MW of juice over 10KM of distance could possibly considered a lightweight matter. This little helicopter contraption will need to generate power AND have enough energy to remain aloft under the weight of that cable. I think it's an interesting concept, but the solution to all our future power woes? Enh. While we're dreaming big, I'd be more interested in this Energy Island [soton.ac.uk] concept being built out.

On second thought, if anyone here has the knowledge to calculate the cable size to carry 10MW and can figure the cable weight per meter and multiply by 10,000 of those... to determine how much weight this device must suspend, I think you have to double it because the ground line has to be able to carry the same amount of power. This isn't an issue for terrestrial power plants because they're ON the ground. But something up in the sky will need to be connected to ground to complete the circuit... is this cra

It just so happens I have a bit of experience designing aluminum and graphite aircraft parts, and my brother is an EE so by osmosis I know enough electrical stuff to fake some calculations.

Thing is, for a constant-diameter cable of a given density and a given strength, the length that can hang under it's own weight is an intrinsic property. For example, I would guess electrical grade (fairly pure) aluminum has a strength of at most 10,000 psi, and a density of.1 lb/in^3. The maximum hanging length would be 1.6 miles. If you taper it you might double that.

That doesn't even include the pulling loads from the monster at the top, which would be large. So aluminum is out.

Carbon nonotubes are hocus-pocus for real-world stuff right now, so forget about that.

However, graphite fibers conduct electricity not too bad, they might work, and they have fabulous strength in tension.

You could probably load a carbon fiber cable up to at least 100,000 psi, and it's density is.06 lb/in^3. That gives a hanging length of 26 miles. That looks better.

Let's fake an electrical calculation to see if it has a chance to work as a transmission cable.

If we use 10KV then for 10MW we have 1000A. The resistivity of graphite fibers is about 4 micro ohms-in. So lets say we make a 1 in^2 section cable, the resistance would be 4 micro-ohms/inch. A 10 mile length would have a resistance of 2.5 ohms and the power dissipation would be 2,500 watts. Surely we could dissipate that over about 10 miles without it overheating the cable.

The weight of the cable would be 1*10*5280*12*.06 = 38,016 lbs (19 tons). Since you need two of them, the total cable-weight load on the monster would be 38 tons.

Add to that the air loads of the horizontal windmill action (which is the whole point of the stupid thing) and what I'll call the catenary multiplier effect for lack of a better term, and the actual load on the cables will probably be something on the order of 100 tons. Since the cables were only stressed to about half their capabilities by the hanging load, it might work.

But you see why I call it a monster. The rotors have to genterate 100 tons of (inclined) lift.

(I used a 10 mile cable length throughout because while the altitude is about 6 miles, the monster is blown sideways and the cable hangs in a catenary shape.)

"KiteGen [sequoiaonline.com]", a kite-driven rotating carousel generating electricity. The kites, at altitudes up to 2Km, could be quickly maneuvered to avoid aircraft, even individual birds. An initial cost of 360,000 euros for a 100m model could generate.5Gw of electricity. A 2 Km version could generate 5 Gw. A proposed initial site is the former Trino Vercellese [keyhole.com] nuclear power plant, already a no-fly zone.

Interesting ideas, all, but access to the jet stream is a big deal requiring big bucks. I'm wondering about small projects.

When I was a kid, I got one of those big, plastic "bat" kites. (They were new on the U.S. toy market at the time, so that tells you how old I am.) I found it horrifically unstable, so I attached a tail made of torn cloth and other stuff. It was quite long and weighed several pounds, making the kite a pain to launch. Once it had gained some altitude, though, it was stable and pulled steadily. I ran out of kite twine, so I drove a stake in the ground and tied it off. Then I rooted around in the garage and found a giant spool of 100lb test fishing line. (Why we had it since it had been years since we'd lived near the Gulf Coast and gone offshore fishing, I didn't know.) I attached this new line to the kite string and let it play out. Quick as a wink, that kite was hundreds of yards high, just hanging there, pulling hard and steady. My older sis had a party that night and all the high school boys wanted to show off how manly they were, so they pulled in the kite for me. They had to work hard for over an hour, pulling it in as fast as they could, to get it to the ground. They were tired, sweaty, and pissed at me by the time they were finished.

I haven't thought about that episode in years. I wonder, though, if it would be possible to put up a fairly large kite to an altitude of just a few hundred yards and keep it aloft (semi-)long term with some sort of small wind generator hanging from it (I know that kite I launched in my youth could have held up 20 or 30 pounds, easily, once it was in the air.) and a small cable leading back to the ground. I live in a fairly mild climate and could pull it in if the weather got bad. I'm just wondering if this could produce enough energy to bank to some batteries that the exercise would be worthwhile.

I know lots of people have tried to go off the grid using power generated from small, often home-built terrestrial windmills. Because the wind at ground level is capricious, they need to feed big battery banks to tide them over the inevitable down time. I'm just wondering if putting a small windmill up at an altitude where air movement is more reliable could actually be a workable approach to the problem.

Of course, this is all just an unformed idea from someone who knows nothing about this stuff. For all I know, the wind at 1000 feet is no more reliable than the wind at ground level and that's why TFA is talking about getting up into the jet stream. Still, it's an intriguing idea to me.

So don't RTFA (I haven't:) ), but make some estimate in your head of the total percent of the energy in the jet stream they could possibly harvest. I have some idea the scales involved and the efficiency of wind turbines, and in my wildest speculations I can't see how they are going to make even a tenth of a percent difference in the strenght of the stream. It's not going to be a problem.

Update: Just for kicks, I Read The Fine Article. In it, it is estimated that 1% of the power in the jet stream would power the entirety of human civilization. Not that you'd ever get that much, but again, not a problem.

This is a terrible idea. Harnessing wind down by the ground is local, but sucking energy out of the jet stream will cause problems "down stream". Operate a sizable "facility", sit back, and watch the "unintended side effects" proliferate.

You're right. We should stick to burning coal, firing gas, building dams, and fissioning radioactive materials. Those have all proven to have no unintended consequences.

We should stick to burning coal, firing gas... Those have all proven to have no unintended consequences.

Actually, I wonder if wind farms could be the solution to Global Warming. I mean, energy can be neither created nor destroyed, right? If they take energy out of the atmosphere, doesn't that absorb at least some of the energy the additional CO2 retains?

Most of the energy humans use is returned right back into the atmosphere either as heat or simple particle motion. Cars heat the air and fight against nonmoving air, computers produce heat and light, and feeding people allows them to create heat, for examples.

Wind power results in a net cost to the level of atmospheric energy. Any attempt to harness wind power extracts energy from the atmosphere and redirects it to human ends. On a small scale, that is no problem. On a large scale, like the bizarre concept represented in this post, the consequences on the planet would be unpredictable and eventually potentially harmful.

By necessity, any generation of electricity is going to remove energy from our environment somehow. (In the case of fossil fuels, this is stor

Birth control? I think it's a little late if you want to manage resources by population reduction. Think more along the lines of 1943 in Poland.To get pollution and resource consumption down to "sustainable" levels where waste products are natually recycled again we need to cut the population to no more than 200 million people. And that is assuming a high level of technology to support that many. Without a lot of technology, maybe more like 50 million is realistic.

Birth control well said. We first need to shoot every economist who still says that no growth is bad and then every idiot who calls me a Luddite. Reducing the population of worlds worst pest will do wonders to our world problems. (No I won't leave first but I do only have one child.)Secondly taking energy out of the antmosphere is a great thing. The global warming (I there is such a thing because New Zealand has been cooling 0.9 degrees centigrade over the last decade)puts energy into the atmosphere and win

I do believe much of the status is self-conceived more than socially conferred (ie, these people are driven by the need to feel better than others, to exult in the moral superiority obtained by having acted righteously or refrained from sin, etc.), though they tend to find each other and build echo chambers to validate these inner assessments (how much of the internet can be described this way...?)

Um, no it doesn't. Just because you made a stupid mistake doesn't mean you shouldn't call out your neighbors when they repeat your stupid mistake. We (the USA) made our mistakes decades or even generations ago; other countries should be acting smart and learning from our mistakes, not acting stupid and repeating them.Your argument is like saying the US shouldn't speak out against slavery in other countries just because we had slavery here 150 years ago. Taken to an extreme, this means no one can criticiz

The challenge is just to harness the good parts of living densely (variety, convenience, returns to scale, etc.) while controlling the bad parts (attractiveness to criminals, incivility, noise, etc.)

I'm not sure how they do that in those high-cost areas you mention (Tokyo, Monaco, NYC), although I'd be interested to find out. Here in my middle-class subdivision where houses cost a measly $250k, it seems that people just can't stand to be quiet, and have to make all the noise they possibly can, whether with

Not sure about this, 10km sounds infinitely doable to me, unlike the distances required for a space elevator.
The article made it sound like the biggest obstacle is the engineering to minimise maintenance, which sounds about right.

"Stabilising and directing a conventional helicopter requires that the pitch of the individual blades be adjusted with every rotation--up to a thousand times a minute. That puts massive stress on the turning mechanism and wears it out rapidly. On a four-rotor arrangement, you can achieve the same effect by changing the pitch of one or two whole rotors, rather than adjusting the pitch of individual blades. Mr Shepard reckons that this will make a big difference..."

From a rotational dynamics viewpoint, changing the axis of rotation of massive rotors will be harder & slower than adjusting the pitch of helicopter blades. I imagine it would be tricky to reorient the axes fast enough to keep the kite attitude under control. Maybe braking or accelerating them would be easier, or having a bunch of auxiliary powered rotors. Hey that's my idea eh. Hereby I claim prior art.

The Space Elevator relies on a carbon nanotube composite material. Nanotubes have already been produced in quantity, and scaling this up to make the SE cable is not that far off. However, I don't recall any requirement that the cable be cheap. With a single Space Shuttle mission costing $450 million, the cable could cost $5 billion to make and install and it would still pay for itself pretty quickly (that's only about 10 missions).The economics for this flying power station are probably a little more lim